Machinery brakes are generally used in mechanical engineering for braking rotating motors or machine parts.
A normally-closed machinery brake refers to the type of machinery brake that has at least one magnetizing coil, which when it is energized the closed machinery brake opens and when it is de-energized the opened machinery brake closes and remains closed, usually when forced by the spring force bringing about the closing. The opposite of a normally-closed machinery brake can be regarded as a normally open machinery brake, which is closed by energizing the magnetizing coil.
One special application for this type of normally-closed machinery brakes is the operational brakes of elevators. This increases elevator safety, because an elevator car moving up and down in an elevator hoistway must be stopped in the event of an electricity outage. The operational brakes of an elevator are kept closed when the elevator has stopped. The operational brakes of an elevator are opened when the elevator starts moving and are closed when the elevator stops.
In order for a normally-closed machinery brake to react quickly enough for removal of the energization of the magnetizing coil, it is usual for a normally-closed machinery brake to comprise a powerful closing spring. A powerful closing spring takes a moving brake shoe quickly against the brake drum, which can cause a noise that is experienced as disturbing. In order for a powerful closing spring to be compressed for opening the brakes, the brake shoe must be moved with a strong force. The metallic bearer parts of the brake shoe can produce a noise that is experienced as disturbing when the opening movement ends.
For solving the damping problem of the opening noise and closing noise of a normally-closed machinery brake, known in the art is a solution presented in the applicant's international application, which is published as printed publication WO 2012/152998 A2, said solution being the placement of an elastically flexible damper between the frame part of a normally-closed machinery brake and the bearer being moved by an electromagnet in relation to said frame part.
Also known in the art, from Inventio AG's European patent 0 897 371, for solving the damping problem of the opening noise and closing noise of a normally-closed machinery brake, is an elevator brake wherein the desired speed profile for movement of the brake shoes is formed as a function of the position of the brake shoes and the speed of the brake shoes is adjusted to be according to the speed profile by adjusting the current of the magnetizing coil of the brake. The position data of the brake shoe is detected mechanically by means of a potentiometer connected to the bearer plate. This enables the closing of an elevator brake softly.